During room wars, hall members rank their choice of rooms (listing all rooms preferred to their current room), leaving theirs last on the list - no one will ever receive a room worse than their current room. Squatters list their own room, turn in their forms, and are then guaranteed the same room for the following year. You can't squat a room currently occupied as a double as a single. If you are in a double and do not want to be in a double next year, this means that you should list every single on the hall before you list your own room.
New in 2014, hall members can also add overriding conditions to their rankings list. For example, "If Bob isn't in B403 then I don't want B404". These conditions are evaluated when you are placed in a room to ensure that all the conditions are met (within reason).
Among hall members wishing to move, priority is evaluated based on (1) terms spent living on the hall, (2) the number of terms spent at MIT (in increments of semesters - these first two numbers are added together to make a base priority), and (3) consideration of current room size. Transfer student from outside MIT are equalized in MIT-terms with their class. People who have lived in a smaller room during the current year will have higher priority than hall members of the same year/time who are in larger rooms. For hall members who have the same priority (e.g., freshmen living in doubles), priority is randomly established within the group by the hall chairs, and then used for assignment of rooms. Priority for hall members who want a room as a double is the sum of both peoples' base priorities (and then by the larger room size of the two doubling folks).
Room wars is conducted in the spring semester in two sections: first, initial room assignments are determined by the method outlined above; hall members will have roughly a week to return their room forms to the chairs. Then, there is a period determined by the hall chairs in which mini room wars are conducted. If two hall members wish to switch their assigned rooms, they may do so provided that all room neighbors (those next to, across from, and diagonal to) the room agree to the switch -- it is the responsibility of the switching hall members to check in with all neighbors. At the end of the designated period, the hall chairs will declare room wars closed and submit final rooming assignments to the EC RAC.
Below is a chart of 4e room sizes (A is the largest, E is ridiculously small). Not all parts of the hall have all the numbers 401 to 414, so we will denote these nonexistent room sizes as -. Note that Goodale 406 and Walcott 403 are typically doubles. Goodale 405 is the GRT room. Bemis 414 is the network closet. Bemis 403 and 404 have no sinks.